Enceladus

Enceladus is the sixth-largest moon of Saturn and the 18th largest in the Solar System. It is about in diameter, about a tenth of that of Saturn's largest moon, Titan. It is covered by clean, freshly deposited snow hundreds of meters thick, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon reaches only , far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide variety of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrain.

Enceladus was discovered on August 28, 1789, by William Herschel, Cryovolcanoes near the south pole shoot geyser-like jets of water vapour, molecular hydrogen, other volatiles, and solid material, including sodium chloride crystals and ice particles, into space, totalling about per second. More than 100 geysers have been identified. Some of the water vapour falls back as snow, now several hundred metres thick; the rest escapes and supplies most of the material making up Saturn's E ring. According to NASA scientists, the plumes are similar in composition to comets. In 2014, NASA reported that Cassini had found evidence for a large south polar subsurface ocean of liquid water with a thickness of around .

These observations of active cryoeruptions, along with the finding of escaping internal heat and very few (if any) impact craters in the south polar region, show that Enceladus is currently geologically active. Like many other satellites in the extensive systems of the giant planets, Enceladus participates in an orbital resonance. Its resonance with Dione excites its orbital eccentricity, which is damped by tidal forces, tidally heating its interior and driving the geological activity.

Cassini performed chemical analysis of Enceladus's plumes, finding evidence for hydrothermal activity, possibly driving complex chemistry. Ongoing research on Cassini data suggests that Enceladus's hydrothermal environment could be habitable to some of Earth's hydrothermal vent's microorganisms, and that plume-found methane could be produced by such organisms.

History

Discovery

left|thumb|upright|William Herschel, discoverer of Enceladus

Enceladus was discovered by William Herschel on August 28, 1789, during the first use of his new 40-foot telescope, then the largest in the world, at Observatory House in Slough, England. Its faint apparent magnitude (HV = +11.7) and its proximity to the much brighter Saturn and Saturn's rings make Enceladus difficult to observe from Earth with smaller telescopes. Like many satellites of Saturn discovered prior to the Space Age, Enceladus was first observed during a Saturnian equinox, when Earth is within the ring plane. At such times, the reduction in glare from the rings makes the moons easier to observe. Prior to the Voyager missions the view of Enceladus improved little from the dot first observed by Herschel. Only its orbital characteristics were known, with estimations of its mass, density and albedo.

Naming

thumb|upright=0.8|[[John Herschel, the astronomer who suggested that the moons of Saturn be named after the Titans and Giants]]

Enceladus is named after the giant Enceladus of Greek mythology. He chose these names because Saturn, known in Greek mythology as Cronus, was the leader of the Titans.

Geological features on Enceladus are named by the International Astronomical Union (IAU) after characters and places from Richard Francis Burton's 1885 translation of The Book of One Thousand and One Nights. Impact craters are named after characters, whereas other feature types, such as fossae (long, narrow depressions), dorsa (ridges), planitiae (plains), sulci (long parallel grooves), and rupes (cliffs) are named after places. The IAU has officially named 85 features on Enceladus, most recently Samaria Rupes, formerly called Samaria Fossa.

Planetary moons other than Earth's were never given symbols in the astronomical literature. Denis Moskowitz, a software engineer who designed most of the dwarf planet symbols, proposed a Greek epsilon (the initial of Enceladus) combined with the crook of the Saturn symbol as the symbol of Enceladus (16px). This symbol is not widely used.

Orbit and rotation

Enceladus is the second major moon from Saturn. It orbits at from Saturn's center and from its cloud tops, between the orbits of Mimas and Tethys. It orbits Saturn every 32.9 hours, fast enough for its motion to be observed over a single night of observation.

Enceladus is currently in a 2:1 mean-motion orbital resonance with Dione, completing two orbits around Saturn for every one orbit completed by Dione.

Like most of Saturn's larger satellites, Enceladus rotates synchronously with its orbital period, keeping one face pointed toward Saturn. Unlike Earth's Moon, Enceladus does not appear to librate more than 1.5° about its spin axis. However, analysis of the shape of Enceladus suggests that at some point it was in a 1:4 forced secondary spin–orbit libration.

Source of the E ring

thumb|upright=1.2|Enceladus orbiting within [[Rings of Saturn#E Ring|Saturn's E ring]]

Plumes from Enceladus, which are similar in composition to comets,

Mathematical models show that the E ring is unstable, with a lifespan between 10,000 and 1 million years; therefore, particles composing it must be constantly replenished. Enceladus is orbiting inside the ring, at its narrowest but highest density point. In the 1980s, some astronomers suspected that Enceladus is the main source of particles for the ring. This hypothesis was confirmed by Cassini first two close flybys in 2005.

The Cosmic Dust Analyzer (CDA) "detected a large increase in the number of particles near Enceladus", confirming it as the primary source for the E ring.

Visual confirmation of venting came in November 2005, when Cassini imaged geyser-like jets of icy particles rising from Enceladus's south polar region.)

Physical characteristics

Shape and size

thumb|Enceladus compared to [[1 Ceres and the Moon]]

Enceladus is a relatively small satellite composed of ice and rock. It is a scalene ellipsoid in shape; its diameters, calculated from images taken by Cassini ISS (Imaging Science Subsystem) instrument, are between the sub- and anti-Saturnian poles, between the leading and trailing hemispheres, and between the north and south poles.

Internal structure

Before the Cassini mission, little was known about the interior of Enceladus. However, flybys by Cassini provided information for models of Enceladus's interior, including a better determination of the mass and shape, high-resolution observations of the surface, and new insights on the interior.

Initial mass estimates from the Voyager program missions suggested that Enceladus was composed almost entirely of water ice. These radionuclides, like aluminium-26 and iron-60, have short half-lives and would produce interior heating relatively quickly. Without the short-lived variety, Enceladus's complement of long-lived radionuclides would not have been enough to prevent rapid freezing of the interior, even with Enceladus's comparatively high rock–mass fraction, given its small size.

Given Enceladus's relatively high rock–mass fraction, the proposed enhancement in 26Al and 60Fe would result in a differentiated body, with an icy mantle and a rocky core. Subsequent radioactive and tidal heating would raise the temperature of the core to 1,000 K, enough to melt the inner mantle. For Enceladus to still be active, part of the core must have also melted, forming magma chambers that would flex under the strain of Saturn's tides. Tidal heating, such as from the resonance with Dione or from libration, would then have sustained these hot spots in the core and would power the current geological activity.

In addition to its mass and modelled geochemistry, researchers have also examined Enceladus's shape to determine if it is differentiated. used limb measurements to determine that its shape, assuming hydrostatic equilibrium, is consistent with an undifferentiated interior, in contradiction to the geological and geochemical evidence. with jets moving 250 kg of water vapour every second Soon after, in 2006 it was determined that Enceladus's plumes are the source of Saturn's E Ring.

Gravimetric data from Cassini December 2010 flybys showed that Enceladus likely has a liquid water ocean beneath its frozen surface, but at the time it was thought the subsurface ocean was limited to the south pole. The top of the ocean probably lies beneath a ice shelf. The ocean may be deep at the south pole.

Measurements of Enceladus's "wobble" as it orbits Saturn—called libration—suggests that the entire icy crust is detached from the rocky core and therefore that a global ocean is present beneath the surface. The amount of libration (0.120° ± 0.014°) implies that this global ocean is about deep. For comparison, Earth's ocean has an average depth of 3.7 kilometres.

The INMS instrument detected mostly water vapour, as well as traces of molecular nitrogen, carbon dioxide, The plumes' composition, as measured by the INMS, is similar to that seen at most comets. as well as larger organics such as benzene (), and complex macromolecular organics as large as 200 atomic mass units, and at least 15 carbon atoms in size.

The mass spectrometer detected molecular hydrogen (H2) which was in "thermodynamic disequilibrium" with the other components, and found traces of ammonia (). The high pH is interpreted to be a consequence of serpentinization of chondritic rock that leads to the generation of H2, a geochemical source of energy that could support both abiotic and biological synthesis of organic molecules such as those that have been detected in Enceladus's plumes.

Further analysis in 2019 was done of the spectral characteristics of ice grains in Enceladus's erupting plumes. The study found that nitrogen-bearing and oxygen-bearing amines were likely present, with significant implications for the availability of amino acids in the internal ocean. The researchers suggested that the compounds on Enceladus could be precursors for "biologically relevant organic compounds".

A 2025 paper reported the detection of organic molecules in plume samples taken by the Cosmic Dust Analyzer.

Possible heat sources

thumb|upright=1.2|Heat map of the south polar fractures, dubbed '[[Tiger stripes (Enceladus)|tiger stripes']]

During the flyby of July 14, 2005, the Composite Infrared Spectrometer (CIRS) found a warm region near the south pole. Temperatures in this region ranged from 85 to 90 K, with small areas showing as high as , much too warm to be explained by solar heating, indicating that parts of the south polar region are heated from the interior of Enceladus. but it cannot explain the source of the heat, with an estimated heat flux of 200 mW/m2, which is about 10 times higher than that from radiogenic heating alone.

Several explanations for the observed elevated temperatures and the resulting plumes have been proposed, including venting from a subsurface reservoir of liquid water, sublimation of ice, decompression and dissociation of clathrates, and shear heating, but a complete explanation of all the heat sources causing the observed thermal power output of Enceladus has not yet been settled.

Heating in Enceladus has occurred through various mechanisms ever since its formation. Radioactive decay in its core may have initially heated it, giving it a warm core and a subsurface ocean, which is now kept above freezing through unidentified mechanisms. Geophysical models indicate that tidal heating is a main heat source, perhaps aided by radioactive decay and some heat-producing chemical reactions. A 2007 study predicted the internal heat of Enceladus, if generated by tidal forces, could be no greater than 1.1 gigawatts, and suggest that it is in thermal equilibrium.

The observed power output of 4.7 gigawatts is challenging to explain from tidal heating alone, so the main source of heat remains a mystery. It is thought that if Enceladus had a more eccentric orbit in the past, the enhanced tidal forces could be sufficient to maintain a subsurface ocean, such that a periodic enhancement in eccentricity could maintain a subsurface ocean that periodically changes in size.

A 2016 analysis claimed that "a model of the tiger stripes as tidally flexed slots that puncture the ice shell can simultaneously explain the persistence of the eruptions through the tidal cycle, the phase lag, and the total power output of the tiger stripe terrain, while suggesting that eruptions are maintained over geological timescales."

Radioactive heating

The present-day radiogenic heating rate is 3.2 ergs/s (or 0.32 gigawatts), assuming Enceladus has a composition of ice, iron and silicate materials. Reducing the freezing point of water with ammonia would also allow for outgassing and higher gas pressure, and less heat required to power the water plumes. The subsurface layer heating the surface water ice could be an ammonia–water slurry at temperatures as low as , and thus less energy is required to produce the plume activity. However, the observed 4.7 gigawatts heat flux is enough to power the cryovolcanism without the presence of ammonia. and scarps were observed. Given the relative lack of craters on the smooth plains, these regions are probably less than a few hundred million years old. The fresh, clean ice that dominates its surface makes Enceladus the most reflective body in the Solar System, with a visual geometric albedo of 1.38

Some areas contain no craters, indicating major resurfacing events in the geologically recent past. There are fissures, plains, corrugated terrain and other crustal deformations. Several additional regions of young terrain were discovered in areas not well imaged by either Voyager spacecraft, such as the bizarre terrain near the south pole.

Impact craters

thumb|A close-up picture of [[Al-Haddar (crater)|Al-Haddar (top), Shahrazad (middle) and Dunyazad (bottom) craters]]

Impact cratering is a common occurrence on many Solar System bodies. Much of Enceladus's surface is covered with craters at various densities and levels of degradation. This subdivision of cratered terrains on the basis of crater density (and thus surface age) suggests that Enceladus has been resurfaced in multiple stages. Viscous relaxation allows gravity, over geologic time scales, to deform craters and other topographic features formed in water ice, reducing the amount of topography over time. The rate at which this occurs is dependent on the temperature of the ice: warmer ice is easier to deform than colder, stiffer ice. Viscously relaxed craters tend to have domed floors, or are recognized as craters only by a raised, circular rim. Dunyazad crater is a prime example of a viscously relaxed crater on Enceladus, with a prominent domed floor.

Tectonic features

thumb|A close-up view of Enceladus's ridges

Voyager 2 found several types of tectonic features on Enceladus, including troughs, scarps, and belts of grooves and ridges.

Evidence of tectonics on Enceladus is also derived from grooved terrain, consisting of lanes of curvilinear grooves and ridges. These bands, first discovered by Voyager 2, often separate smooth plains from cratered regions.

Another example of tectonic features on Enceladus are the linear grooves first found by Voyager 2 and seen at a much higher resolution by Cassini. These linear grooves can be seen cutting across other terrain types, like the groove and ridge belts. Like the deep rifts, they are among the youngest features on Enceladus. However, some linear grooves have been softened like the craters nearby, suggesting that they are older. Ridges have also been observed on Enceladus, though not nearly to the extent as those seen on Europa. These ridges are relatively limited in extent and are up to one kilometre tall. One-kilometer high domes have also been observed.

South polar region

thumb|upright=1.35|An atlas of Enceladus's south pole quadrangle, which is dominated by the [[Tiger stripes (Enceladus)|tiger stripes]]

Images taken by Cassini during the flyby on July 14, 2005, revealed a distinctive, tectonically deformed region surrounding Enceladus's south pole. This area, reaching as far north as 60° south latitude, is covered in tectonic fractures and ridges. The area has few sizeable impact craters, suggesting that it is the youngest surface on Enceladus and on any of the mid-sized icy satellites. Modelling of the cratering rate suggests that some regions of the south polar terrain are possibly as young as 500,000 years or less. They appear to be the youngest features in this region and are surrounded by mint-green-colored (in false colour, UV–green–near IR images), coarse-grained water ice, seen elsewhere on the surface within outcrops and fracture walls. VIMS also detected simple organic (carbon-containing) compounds in the tiger stripes, chemistry not found anywhere else on Enceladus thus far.

One of these areas of "blue" ice in the south polar region was observed at high resolution during the July 14, 2005, flyby, revealing an area of extreme tectonic deformation and blocky terrain, with some areas covered in boulders 10–100 m across.

The boundary of the south polar region is marked by a pattern of parallel, Y- and V-shaped ridges and valleys. The shape, orientation, and location of these features suggest they are caused by changes in the overall shape of Enceladus. As of 2006 there were two theories for what could cause such a shift in shape: the orbit of Enceladus may have migrated inward, leading to an increase in Enceladus's rotation rate. Such a shift would lead to a more oblate shape; and a maximum velocity of . Cassini UVIS later observed gas jets coinciding with the dust jets seen by ISS during a non-targeted encounter with Enceladus in October 2007.

The combined analysis of imaging, mass spectrometry, and magnetospheric data suggests that the observed south polar plume emanates from pressurized subsurface chambers, similar to Earth's geysers or fumaroles.

The intensity of the eruption of the south polar jets varies significantly as a function of the position of Enceladus in its orbit. The plumes are about four times brighter when Enceladus is at apoapsis (the point in its orbit most distant from Saturn) than when it is at periapsis. This is consistent with geophysical calculations which predict the south polar fissures are under compression near periapsis, pushing them shut, and under tension near apoapsis, pulling them open. Strike-slip tectonics may also drive localized extension along alternating (left- and right- lateral) transtensional zones (e.g., pull-apart basins) over the Tiger Stripes, thereby regulating jet activity within these regions.

Much of the plume activity consists of broad curtain-like eruptions. Optical illusions from a combination of viewing direction and local fracture geometry previously made the plumes look like discrete jets.

The extent to which cryovolcanism really occurs is a subject of some debate. At Enceladus, it appears that cryovolcanism occurs because water-filled cracks are periodically exposed to vacuum, the cracks being opened and closed by tidal stresses.

Origin

Mimas–Enceladus paradox

Mimas, the innermost of the round moons of Saturn and directly interior to Enceladus, is a geologically dead body, even though it should experience stronger tidal forces than Enceladus. This apparent paradox can be explained in part by temperature-dependent properties of water ice (the main constituent of the interiors of Mimas and Enceladus). The tidal heating per unit mass is given by the formula

:<math>q_{tid}=\frac{63\rho n^{5} r^{4} e^{2{38\mu Q},</math>

where ρ is the (mass) density of the satellite, n is its mean orbital motion, r is the satellite's radius, e is the orbital eccentricity of the satellite, μ is the shear modulus and Q is the dimensionless dissipation factor. For a same-temperature approximation, the expected value of qtid for Mimas is about 40 times that of Enceladus. However, the material parameters μ and Q are temperature dependent. At high temperatures (close to the melting point), μ and Q are low, so tidal heating is high. Modelling suggests that for Enceladus, both a 'basic' low-energy thermal state with little internal temperature gradient, and an 'excited' high-energy thermal state with a significant temperature gradient, and consequent convection (endogenic geologic activity), once established, would be stable. Additional historical information is needed to explain how Enceladus first entered the high-energy state (e.g. more radiogenic heating or a more eccentric orbit in the past).

The significantly higher density of Enceladus relative to Mimas (1.61 vs. 1.15 g/cm3), implying a larger content of rock and more radiogenic heating in its early history, has also been cited as an important factor in resolving the Mimas paradox.

It has been suggested that for an icy satellite the size of Mimas or Enceladus to enter an 'excited state' of tidal heating and convection, it would need to enter an orbital resonance before it lost too much of its primordial internal heat. Because Mimas, being smaller, would cool more rapidly than Enceladus, its window of opportunity for initiating orbital resonance-driven convection would have been considerably shorter. It suggests that tectonics in the south polar region is probably mainly related to subsidence and associated subduction caused by the process of mass loss.

Date of formation

In 2016, a study of how the orbits of Saturn's moons should have changed due to tidal effects suggested that all of Saturn's satellites inward of Titan, including Enceladus (whose geologic activity was used to derive the strength of tidal effects on Saturn's satellites), may have formed as little as 100 million years ago.

A later study from 2019 estimated that the ocean is around one billion years old.

Potential habitability

Enceladus ejects plumes of salted water laced with grains of silica-rich sand, nitrogen (in ammonia), This indicates that hydrothermal activity —an energy source— may be at work in Enceladus's subsurface ocean. Models indicate that the large rocky core is porous, allowing water to flow through it, transferring heat and chemicals. This was confirmed by observations and other research. Molecular hydrogen (), a geochemical source of energy that can be metabolized by methanogen microbes to provide energy for life, could be present if, as models suggest, Enceladus's salty ocean has an alkaline pH from serpentinization of chondritic rock. are of great interest in astrobiology and the study of potentially habitable environments for microbial extraterrestrial life. Geochemical modelling results before the detection of phosphorus indicated that Enceladus met potential abiogenesis-requirements.

In June 2023, astronomers reported that phosphates had been detected on Enceladus, completing the set of basic chemical ingredients for life there.

The presence of a wide range of organic compounds and ammonia indicates their source may be similar to the water/rock reactions known to occur on Earth and that are known to support life. Therefore, several robotic missions have been proposed to further explore Enceladus and assess its habitability. Some of the proposed missions are: Journey to Enceladus and Titan (JET), Enceladus Explorer (En-Ex), Enceladus Life Finder (ELF), Life Investigation For Enceladus (LIFE), and Enceladus Life Signatures and Habitability (ELSAH).

Hydrothermal vents

[[File:PIA19058-SaturnMoon-Enceladus-PossibleHydrothermalActivity-ArtistConcept-20150311.jpg|thumb|An artist's impression of possible hydrothermal activity on Enceladus's ocean floor

The presence of ample hydrogen in Enceladus's ocean means that microbes – if any exist there – could use it to obtain energy by combining the hydrogen with carbon dioxide dissolved in the water. The chemical reaction is known as "methanogenesis" because it produces methane as a byproduct, and is at the root of the tree of life on Earth, the birthplace of all life that is known to exist.

Exploration

Voyager missions

thumb|Voyager 2<nowiki/>'s image mosaic of Enceladus

The two Voyager spacecraft made the first close-up images of Enceladus. Voyager 1 was the first to fly past Enceladus, at a distance of 202,000 km on November 12, 1980. Images acquired from this distance had very poor spatial resolution, but revealed a highly reflective surface devoid of impact craters, indicating a youthful surface. Voyager 1 also confirmed that Enceladus was embedded in the densest part of Saturn's diffuse E ring. Combined with the apparent youthful appearance of the surface, Voyager scientists suggested that the E ring consisted of particles vented from Enceladus's surface.

Voyager 2 passed closer to Enceladus (87,010 km) on August 26, 1981, allowing higher-resolution images to be obtained. They also revealed a surface with different regions with vastly different surface ages, with a heavily cratered mid- to high-northern latitude region, and a lightly cratered region closer to the equator. This geologic diversity contrasts with the ancient, heavily cratered surface of Mimas, another moon of Saturn slightly smaller than Enceladus. The geologically youthful terrains came as a great surprise to the scientific community, because no theory was then able to predict that such a small (and cold, compared to Jupiter's highly active moon Io) celestial body could bear signs of such activity.

Cassini

thumb|A picture of Enceladus in parallel with Saturn's ring, taken by Cassini in January 2006

The answers to many remaining mysteries of Enceladus had to wait until the arrival of the Cassini spacecraft on July 1, 2004, when it entered orbit around Saturn. Given the results from the Voyager 2 images, Enceladus was considered a priority target by the Cassini mission planners, and several targeted flybys within 1,500 km of the surface were planned as well as numerous, "non-targeted" opportunities within 100,000 km of Enceladus. The flybys have yielded significant information concerning Enceladus's surface, as well as the discovery of water vapour with traces of simple hydrocarbons venting from the geologically active south polar region.

These discoveries prompted the adjustment of Cassini flight plan to allow closer flybys of Enceladus, including an encounter in March 2008 that took it to within 48 km of the surface. Cassini performed a flyby on October 28, 2015, passing as close as and through a plume. Confirmation of molecular hydrogen () would be an independent line of evidence that hydrothermal activity is taking place in the Enceladus seafloor, increasing its habitability.

On December 14, 2023, astronomers reported the first time discovery, in the plumes of Enceladus, of hydrogen cyanide, a possible chemical essential for life as we know it, as well as other organic molecules, some of which are yet to be better identified and understood. According to the researchers, "these [newly discovered] compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life."Enceladus Explorer (EnEx), a lander funded by the German Aerospace Center to study the habitability potential of its subsurface ocean, and two astrobiology-oriented mission concepts, the Enceladus Life Finder (ELF) and Life Investigation For Enceladus (LIFE).

The European Space Agency (ESA) was assessing concepts in 2008 to send a probe to Enceladus in a mission to be combined with studies of Titan: Titan Saturn System Mission (TSSM). TSSM was a joint NASA/ESA flagship-class proposal for exploration of Saturn's moons, with a focus on Enceladus, and it was competing against the Europa Jupiter System Mission (EJSM) proposal for funding. In February 2009, it was announced that NASA/ESA had given the EJSM mission priority ahead of TSSM, although TSSM will continue to be studied and evaluated.

In November 2017, Russian billionaire Yuri Milner expressed interest in funding a "low-cost, privately funded mission to Enceladus which can be launched relatively soon." In September 2018, NASA and the Breakthrough Initiatives, founded by Milner, signed a cooperation agreement for the mission's initial concept phase. The spacecraft would be low-cost, low mass, and would be launched at high speed on an affordable rocket. The spacecraft would be directed to perform a single flyby through Enceladus's plumes in order to sample and analyse its content for biosignatures. NASA provided scientific and technical expertise through various reviews, from March 2019 to December 2019.

In 2022, the Planetary Science Decadal Survey by the National Academy of Sciences recommended that NASA prioritize its newest probe concept, the Enceladus Orbilander, as a Flagship-class mission, alongside its newest concepts for a Mars sample-return mission and the Uranus Orbiter and Probe. The Enceladus Orbilander would be launched on a similarly affordable rocket, but would cost about $5 billion, and be designed to endure eighteen months in orbit inspecting Enceladus's plumes before landing and spending two Earth years conducting surface astrobiology research.

In 2024, ESA named a mission to Enceladus its top priority. Currently known as the L4 mission, it is an orbiter and lander proposed for launch in 2042, with arrival at Enceladus in 2053.

| 2006 || NASA || 'Titan and Enceladus $1B Mission Feasibility' Study || Not selected ||

| 2007 || NASA || 'Enceladus Flagship' study || Not selected ||

| 2008 || NASA/ESA || TandEM became Titan Saturn System Mission (TSSM) || Not selected ||

| 2011 || NASA JPL || Journey to Enceladus and Titan (JET) || Not selected ||

| 2012 || DLR || Enceladus Explorer (EnEx) lander, employing the IceMole || Not selected ||

| 2012 || NASA JPL || Life Investigation For Enceladus (LIFE) || Not selected ||

| 2015 || NASA JPL ||Enceladus Life Finder (ELF) || Not selected ||

| 2017 || ESA/NASA || Explorer of Enceladus and Titan (E2T) || Not selected ||

| 2017 || NASA || Enceladus Life Signatures and Habitability (ELSAH) || Not selected ||

| 2017 || Breakthrough Initiatives || Breakthrough Enceladus mission || Proposed ||

| 2022 || NASA || Enceladus Orbilander || Proposed ||

| 2024 || ESA || L4, lander and orbiter || Proposed ||

| 2025 || CNSA || Unnamed mission || Proposed ||

References

Informational notes

Citations

External links

Enceladus Profile at NASA's Solar System Exploration site
Calvin Hamilton's Enceladus page
The Planetary Society: Enceladus blogs
CHARM: Cassini–Huygens Analysis and Results from the Mission page, contains presentations on Enceladus results
Paul Schenk's 3D images and flyover videos of Enceladus and other outer solar system satellites
Dr. Alfonso Davila's public talk on Enceladus in the Silicon Valley Astronomy Lectures
Habitability of Enceladus: Planetary Conditions for Life

; Images

Cassini images of Enceladus
Images of Enceladus at JPL's Planetary Photojournal
Movie of Enceladus's rotation from the National Oceanic and Atmospheric Administration
Enceladus global and polar basemaps (December 2011) from Cassini images
Enceladus atlas (May 2010) from Cassini images
Enceladus nomenclature and Enceladus map with feature names from the USGS planetary nomenclature page
Google Enceladus 3D, interactive map of the moon
Image album by Kevin M. Gill